Electron beam convergence apparatus



June 28, 1966 w. F. DIETz 3,258,642

ELECTRON BEAM CONVERGENCE APPARATUS Filed Aug. 5, 196.3 2 Sheets-Sheet 1 il f3 June 28, 1966 w. F. DlETz ELECTRON BEAM CONVERGENCE APPARATUS 2 Sheets-Sheet 2 Filed Aug. 5, 1965 INVENTOR. Maz/wi /frz BY W I Md IJ United States Patent O 3,258,642 ELECTRN BEAM CQNVERGENCE APPARATUS Wolfgang F. Dietz, lntlianapoiis, Intl., assignor to Radio Corporation of America, a corporation of Deiaware Filed Aug. 5, 1963, Ser. No. 299,728 12 Claims. (Si. S15-22) This invention relates to color image display systems and particularly to means `for making a plurality of electron beams of a multiple beam display device converge at all scanned points on the target electrode of said device.

An illustrative example of such a multiple beam display device is a color kinescope, Color kinescopes of the shadow mask type normally have three electron guns positioned in the neck of the kinescope and a tar-get electrode including an apertured s-hadow mask located between the electron guns and a luminescent screen of phosphor dots. The dots are arranged in groups of three in register with respective apertures of the mask. Static magnetic means are provided for making the three electron beams converge at the center of the scanned area of the target electrode. The three beams, after passing through the shadow mask, respectively strike three phosphor dots, each emittin-g light of a different color. All three bea-ms are defiected by a common horizontal and vertical deflection system so that the beams systematically scan the kinescope target. The more the three beams are deflected from the center of the target, unless corrective measures are taken, the greater may be the misconvergence of the beams when they reach the shadow mask. lt is, therefore, customary to provide dynamic electromagnetic means for correcting the misconvergence of the beams as a function of the angular deflection of the beams form the center of the kinescope tar-get. For this purpose, current waveforms of generally parabolic shape are derived from the horizontal and vertical deection circuits and are employed, in conjunction with three convergence electromagnets, to dynamically converge the three beams at all points of the entire scanned area of the kiuescope target.

The waveforms employed must have :proper shapes in order to achieve good convergence of the three beams at all points ofthe kinescope target. rllhe waveform requirements ymay be estimated by observing the unconverged rasters of the three beams. It -has been observed that color picture tube systems operating with relatively large angles of deection, as for example 90, require more c-orrection at the outer edges of the scanned area when the undeected beams are statically converged at the center of the picture area. Because of this requirement, the dynamic waveform must have greater amplitude and precision in order to effect satisfactory convergence throughout the scanned picture area. Not only are the waveshaping requirements more severe in more recent systems having greater angles of beam deflection, but also considerably more deflecting force is needed to suitably effect the desired beam convergence.

Recent trends in the design of color television receivers have been to employ dynamic beam convergence circuits which include no active elements. Such circuits perfo-rm essentially the function of providing suitably shaped waves for application to the convergence electromagnets. The energy for these electromagnets consequently -must come entirely from the horizontal and vertical deflection circuits. As the angle of beam deflection increases, more energy is required to effect the deliection. Similarly, still more energy must be supplied to effect the desired convergence of the bea-ms. Such requirements have placed severe burdens upon the deflecting circuits, particularly the horizontal deflection circuit.

In such convergence circuits it is customary to desire relatively short duration pulses from the horizontal deflection circuit and to perform a double integration upon these pulses to ultimately provide the desired substantially parabolic waves for energizing the convergence electromagnets. The pulses are .first integrated to provide a substantially sawtooth wave shape and the sawtooth waves are themselves integrated to the substantially parabolic wave shape. Usually, in convergence circuits operating at the vertical deflection rate, a substantially sawtooth wave is derived from the vertical deflection circuit :and it is integrated to the desired substantially parabolic waveform.

Therefore, it is an object of the invention to provide an improved high efiiciency circuit by which to effect convergence of a plurality of electron beams of a color kinescope throughout a raster produced by relatively wide angle deflection of said beams.

The present invention reduces the energy demands placed upon the deflection circuits by providing active circuit elements (e.g., transistors) in the convergence circuits which elements themselves consume substantially no energy. At each of the horizontal and vertical deflection frequencies the substantially parabolic convergence Waves are produced by deriving substantially sawtooth waves from the respective deflection circuits. The active circuit elements controlled by these sawtooth Waves drive sufficient energy, provided from a local power supply, through the convergence electromagnets and associated circuits to produce the desired parabolic waves.

The parabolic wave shaping is achieved at the horizontal deection rate by energizing the convergence electromagnets during one portion of the cycle and allowing such energy to excite an auxiliary wave shaping network during another portion of the cycle so that the overall result is the traversal of the electromagnet energizing windings by substantially parabolic waves of suitable amplitude and phasing to effect the desired dynamic beam convergence.

More particularly, the invention is embodied in a system utilizing transistors included in coupling means between the deflection circuits and the convergence electromagnets. Each of these electromagnets has a single winding traversed both by horizontal and vertical frequency convergence current waves. The coupling means includes facilities for mutually isolating the horizontal and vertical deflection systems.

The convergence circuits include wave shaping networks of such a character as to provide the convergence parabolic current waves with steeper sides than heretofore has been used in order to provide better beam convergence at the edges of the picture area for a kinescope operating with (or more) beam defiection. These wave shaping circuits have such time constants that there is little or no current flowing through the electromagnet windings at the center of each horizontal beam trace. Also, the wave shaping circuits may be provided with facilities for preventing current flow therethrough while the driving transistor is conductive.

For a better understanding of the invention together with additional objects, features and advantages thereof, reference now will be made to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a block diagram of a color television receiver in which the present invention may be embodied;

FIGURE 2 is a schematic circuit diagram representing the dynamic beam convergence system embodying the invention; and

FIGURE 3 is a set of curves for reference in describing the operation of the invention.

Reference rst is made to FIGURE l for a general description of a color television receiver embodying the present invention. Radiated signals received by the antenna 11 are processed in the TV receiver circuits i2 in a known manner to produce (1) video signals representing three component colors of an image to be reproduced and (2) synchronizing signals for controlling beam deflection and for other purposes such as the production of suitable signals by which to effect convergence of the three electron beams at the target electrode of the image-reproducing color kinescope. The receiver circuits 12 may be of the type disclosed in Color Telcvision Service Data-1961, No. T6 furnished by RCA Sales Corporation, Indianapolis, Indiana.

The color television receiver also includes a three-beam color kinescope 13 serving as a color image-reproducing device such as a shadow mask color kinescope of the RCA type 21FBP22 or 2lFJP22 `for example. The red, green and blue representative signals received from the receiver circuits 12 are impressed respective upon electron guns 14, 15 and 16 of the tri-color kinescope 13. The three electron beams produced by these guns are deflected together over the target screen of the kinescope under the control of a deflection yoke 17. The beams are maintained in convergence with each other by means of a suitably energized beam convergence yoke 18, an illustrative form of which will be described subsequently.

Also derived Ifrom the receiver circuits 12 are horizontal and vertical synchronizing signals which are impressed upon a synchronizing signal separator 19. The horizontal synchronizing signals are impressed upon the horizontal deflection circuit 21 and the vertical synchronizing signals are impressed upon the vertical deflection circuit 22. The horizontal and vertical deflection circuits are connected to the deflection yoke 17 as indicated by the reference characters H-H and V-V. All of the apparatus of FIGURE 1 described up to this point may be of the same character as that disclosed in the service data previously referred to.

Signals derived from the horizontal deflection circuit 21 at the horizontal deflection rate are impressed upon horizontal convergence circuits 23, the ouput of which is connected to the electromagnets of the convergence yoke 18. Details of such convergence circuits by which suitable convergence waves are produced will be described subsequently. Signals as the vertical deflection rate derived from the vertical deflection circuit 22 are impressed upon the vertical convergence circuits 24 for the production of suitable waves which also are impressed upon the electromagnets of the convergence yoke f6.

The vertical convergence circuits are not part of the present invention and may be of a known type such as disclosed in Patent No. 2,903,622 granted September S, 1959 to J. C. Schopp.

Reference now is made to FIGURE 2 for descriptions (l) of the physical relationship of the convergence electromagnets and the electron beams controlled respectively thereby as presently embodied in commercial color television receivers such as that disclosed in the referenced RCA Service data and (2) of the electromagnet energizing circuits embodying the invention. In the center of ligure is a transverse sectional view of the neck portion of a color kinescope as it appears when Viewed from the luminescent screen end of the kinescope. The three electron beams 25 pass respectively between pairs of pole pieces 26, 27 and Z8 located internally of the neck 29 of the kinescope 13. These pole pieces extend inwardly from the ends of substantially U-shaped cores of green, red and blue convergence electromagnets 31, 32 and 33 respectively mounted externally around the neck of the kinescope. Each of the convergence electromagnets is provided with an energizing winding designated S14-G, 34K and 34B respectively for the green, red and blue electromagnets 31, 32 and 33. Energization of the electromagnet windings produces a magnetic field between the corresponding pole pieces which moves the corresponding electron beam radially. There also may be included as part of the convergence electromagnet structure some means for effecting a static convergence of the electron beams 25. The static convergence means may be permanent magnets associated with the respective convergence electromagnets or may comprise windings on the respective electromagnets for energization by direct current of the proper amplitude and polarity to effect the desired static convergence of the electron beams. Such static convergence means is known and, since a description of it is not needed for an understanding of this invention, it is not shown.

FIGURE 2 also illustrates the horizontal and vertical convergence circuits for energizing the windings of the green, red and blue convergence magnets 31, 32 and 33 respectively. The horizontal convergence circuits will be described first and this description will be separated into two parts; (l) for energizing the green and red electromagnet windings 34G and 34K respectively, and (2) for energizing the blue electromagnet winding 34B.

The horizontal deflection circuit includes a deflection output tube 35 and an output transformer 36. This transformer has a primary winding 37 which is connected in a known manner to the horizontal dellection yoke and to the high voltage rectifier circuits as indicated. The transformer also has a pair of secondary windings 38 and 39 in which voltage pulses at the horizontal repetition rate are developed. These secondary windings are interconnected by a potentiometer 41, the movable contact of which is connected to a positive source of biasing potential indicated at +15 v. the function of which will be described subsequently. Operating voltage for the horizontal output tube 35 is applied to the anode 4-2 through a portion of the primary winding 37 of the output transformer 36 and is derived from the usual boosted B+ supply indicated at -l-BB connected to a terminal of the primary winding in the usual manner. The cathode 43 of the horizontal output tube 35 is connected to ground through a parallel arrangement of two potentiometers 44 and 45. Substantially sawtooth voltage waves are developed in these potentiometers during the second half of each line scanning period when the output tube 35 is conducting in accordance with known reaction scanning principles.

The movable contact 46 of the potentiometer 44 is connected to the base electrode of a driver transistor 47 for the green and red electromagnet windings 34G and 34K respectively. The emitter electrode of this transistor is connected through a resistor 48 to ground. The collector electrode of transistor 47 is connected to an intermediate tap of a variable inductor 49 serving as a differential control by which to suitably apportion a horizontal parabolic current wave between the green and red electromagnet windings 34G and 34K respectively. One terminal of the inductor 49 is connected to a terminal of the red electromagnet winding 34R, the other terminal of this winding 34R being connected to the secondary winding 38 on the horizontal output transformer 36. The second terminal of the inductor 49 is connected to one terminal of the green electromagnet winding 34G, the other terminal of this winding 34G being connected to the movable contact 5t)` of a potentiometer 51. The resistive portion of this potentiometer is connected across a secondary winding 52 of the vertical deflection output transformer 53. The potentiometer 51 and transformer winding 52 are connected to the secondary winding 38 -on the horizontal detlection output transformer 36. A part of the vertical deflection circuit is included in the described circuit for energizing the green and red elcctromagnet windings 34G and 34K respectively by horizontal convergence waves because of the fact that only one winding on each of the convergence magnets is used for both horizontal and vertical convergence energization.

It is seen from the foregoing description of the hori- Zontal convergence circuits for the green and red electromagnets 31 and 32 that the collector electrode of the driver transistor 47 is supplied with positive biasing potential derived from the source connected to the potentiometer 41 through the energizing windings 34G and 34R for the green and red electromagnets. A wave shaping circuit 54 comprising the parallel arrangement of a resistor 55 and a capacitor 56 in series with a potentiometer 57 is effectively connected across the energizing windings 34G and 34R respectively between the collector electrode of the driver transistor 47 and the positive ybiasing potential source as indicated at +15 v. connected to the movable contact of the potentiometer 57.

The movable contact 58 of the potentiometer 45 is connected to the base electrode of a driver transistor 59 for the blue electromagnet winding 34B. The emitter electrode of this transistor is connected through resistor 61 to ground. The collector electrode of this transistor is connected through the blue electromagnet energizing winding 34B to the source of positive biasing potential indicated at y+15 v. This electromagnet winding also is effectively shunted by a wave shaping network 62 cornprising a series combination of a resistor 63 and a diode 64 in parallel with a capacitor 65 and the network further including a potentiometer 66 connected to the -l-lS v. positive biasing potential source.

The circuits for energizing the convergence electromagnet windings at the vertical deflection rate now will be described; rst, for the green and red electromagnets 31 and 32 and second, for the blue electromagnet 33. The vertical deflection circuit includes a deflection output tube 67 and the previously referred to output transformer 53. The anode of the output tube 67 is supplied with operating potential through a primary winding 68 on the output transformer 53 from a positive potential source indicated at +B. The output transformer 53 also has a secondary winding 69 connected to the deflection yoke in the usual manner as indicated.

The cathode circuit of the vertical output tube 67 includes components for wave shaping, biasing and energizing a driver transistor 70. The base of this transistor is biased for conduction principally during the last half of the vertical scanning period by means of a series arrangement of a resistor 71 and the resistive portion of a potentiometer 72 connected to ground from the cathode of the tube 67. Also included in the cathode circuit is a network 73 including the parallel arrangement of a resistor 74 and a capacitor 75, the purpose of which is to suitably proportion the D-.C. and A.C. components of the sawtooth current wave traversing the tube 67 for properly energizing the convergence electromagnet windings at vertical deflection frequency. The magnitude of the energization of the driver transistor 70E is controlled by the adjustment of the potentiometer 72. A diode 76 is connected between the network 73 and the base of the driver transistor 70 for the purpose of auginenting the energization of the transistor during the last stage of the vertical scanning period. A series arrangement of a potentiometer 78 and a capacitor 79 is connected from the base of the transistor to ground for the purpose of converting the substantially sawtooth wave derived from the cathode of the tube 67 into a substantially parabolic wave for energizing the convergence electromagnet windings 34G and 34R. The capacitor 79 effectively integrates the sawtooth wave and the adjustment of the resistor 78 controls the shaping of the resultant parabolic wave.

The emitter of tthe driver transistor 70 is connectedto ground through a resistor 81. The collector of the driver transistor 76) is connected through a choke coil 82 to the intermediate tap on the inductor 419 from which the vertical parabolic wave -iiows through the green and red convergence eleotromragnet windings 34G and 34K respectively, the circuit terminating at the source of posi-tive bia-sing potential +115 v. connected to the potentiometer 41. The choke coil 82 serves to isolate the horizontal and vertical deflection rate driver circuits from one another. A capacitor 83 connected from vthe collector :of the vertical driver transistor 7tl to ground serves to provide additional integration of the vertical sawtooth wave derived from the vertical deliection output turbe 67 so as to provide additional shaping of the parabolic current wave -for traversal of the green and red eleotromagnet windings 34S and 34K respectively.

A-s previously described, the circuit through the green and red electromagnet windings 3'4G and 34R respectively includes the potentiometer I5t1 connected to the secondary winding 52 `of the vertical output transformer 54. The purpose of the inclusion of these circuit components is to introduce a sawtooth wave component at vertical deflection frequency for proper phasing or tilting of Ithe substatnially parabolic fwave through the electromagnet wind-ings. The `amplitude of the sawtooth wave component is determined by the position o-f the movable contact 5t) on the potentiometer 5d.

rIihe adjustment of the potentiometer 72 effectively controls lthe amplitude of both the D.C. and A.C. cornponents of |the parabolic vertical convergence Wave applied to -the green and red electromagnet windings 34G and 34K respectively. By such means, these windings are transversed by currents of approximately lthe same amplitude which, at the midpoint of each vertical deflection cycle, is substantially zero irrespective of the peak-to-peak amplitude of the parabolic waves applied to these windings. The adjustment of the potentiometer 78 determines the proper phasing of the vertical parabolic wave applied to the green and red convergence windings.

No parabolic current wave energy is applied to the blue electromagnet winding 34B. Only a sawtooth wave component is applied to this winding. 'Ilhe sawtooth wave is derived from a secondary winding 84 on the vertical output transformer 53. This winding is connected through a potentiometer y85 and a choke coil 86 to the blue convergence electromagnet winding 34B. The choke coil serves to isolate the horizontal and vertical convergence wave circuits from one another. The potentiometer 85 serves to control the amplitude of l'the sawtooth convergence 'wave applied to the blue conergence eflectrornagnet winding 34B.

For a more detailed description of the operation of the horizontal deflection rate convergence circuits, reference will be made to FIGURE 3 in addition to the circuit diagram of FIGURE 2. The position of the movable contact 46 on the potentiometer 44 controls the peak-to-peak amplitude of the `substantially parabolic current wave impressed upon the green and red convergence electromagnet windings 34G and 34R respectively. in accordance with known reaction scanning principles, :the horizontal output tube 325 is conducting during approxi-mately only the .second half oilf each horizontal deiiection or line trace period. The current through this tube has a substantially saw tooth wave shape thereby developing a substantially 'sawtooth voltage across the potentiometer 44. In FIGURE 3 this sawtooth voltage is represented by the wave 87. I-t is seen |with reference to :the indicated time scale that this sawtooth voltage wave exists only during the second half of each line period. By virtue of the predominantly inductive character of the circuits, including the inductor 49 and the green and red electromagnet windings 34G and 34K respectively, there is developed in the output or collector circuit of the driver transistor 47 a substantially parabolic wave 38 produced by integrating the sawtooth wave `37 and represen-ting the current through the electromagnet windings. This wave is developed effectively 'by storing energy, controlled by the sawtooth wave yS7, in the convergence electrornagnet windings dur- 'ing conduction periods of the driver transistor 47. During non-conducting periods of the driver transistor, which occur in the first half of each horizontal trace period, the stored energy is dissipated in the circuits including the electromagnet windings and the Wave shaping network 54, the parameters and adjustment of the latter being such as to effect substantially complete dissipation of this energy at the middle of each horizontal trace period. In `this way, substantially no current flow through the convergence electromagnet windings at the middle of each horizontal trace period is assured, ir-

" respective of the pcak-to-peak amplitude of the wave S8 of FIGURE 3 as determined by the .adjustment of the potentiometer 44. Suitable shaping of the parabolic wave 88 is effected by the proper adjustment of the potentiometer 57.

The total parabolic current at horizontal deflection rate which is supplied to the green and red electromagnet windings 3'4G and 34R respectively is determined by the adjustment of the potentiometer 44. This total current l-is suitably divided between the two electromagnet windings :to effect the' desired beam convergence by proper adjustment of the inductance 49.

A sawtooth wave component at horizontal deflection frequency is supplied to the green and red electromagnet windings 34G and 34K respectively by the secondary windings 38 and 39 on the horizontal output transformer 36. Pulses are developed in these transformer windings which are integrated by the circuits including the convergence electromagnet windings into substantially sawtooth current waves. The adjustment yof the potentiometer 41 serves to properly proportion the horizontal sawtooth wave components between the two electromag- -net windings.

The operation of the energizing circuits for the blue convergence electromagnet winding 34B is substantially the same as that described for the green and red electromagnet windings. The position of the movable contact 58 on potentiometer 45 determines the peak-to-peak amplitude of the substantially parabolic current wave at horizontal deflection frequency through the blue electromagnet winding. The wave shaping circuit 62, connected effectively across the blue convergence electromagnet winding 34B, is essentially the `same as the corresponding wave shaping network S4 except that a diode 64 is connected in series with resistor 63. The purpose of this diode is to prevent the flow of current through the wave shaping network 62 during periods of conduction of the driver transistor 59. All of the substantially parabolic current derived from the transistor flows through the electromagnet Winding, thereby minimizing the current conducting requirements of the transistor. The polarity of the diode is such that, during the first half of each horizontal trace period in which the transistor 59 is not conducting, current may flow thro-ugh the shaping network in circuit with the electromagnet winding thereby developing the remainder of the parabolic current Wave. A similar diode may be connected, if desired, in series with the resistor 55 of the shaping network 54 thereby lessening current conducting requirements of the driver transistor 47. The final shaping of the para-bolic current wave through the blue convergence electromagnet winding 34B is determined by the adjustment of the potentiometer 66.

What is claimed is:

1. In a television color image display system including a multiple beam color image reproducing device and deflection means for deflecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said beams at all points of said raster comprising;

a dynamic convergence electromagnet having an energizing winding;

a source of `a sawtooth wave;

means including a transistor coupling said source to said winding to impress said sawtooth wave upon said winding only during the latter half of each of said trace periods to store energy in said Winding; and

a wave-shaping circuit connected across said winding to effect a substantially parabolic current flow through said Winding with substantially no current flow at the middle of each of said trace periods.

2. In a television color image display system including a multiple beam color image reproducing device and deflection means for deflecting said beams in a series of vertically spaced horizontal lines during successive beam Etrace periods to form a raster,

the combination tor converging said beams at all points of said raster comprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth wave;

means including a transistor coupling said source to said winding to impress said sawtooth wave upon said winding only during the latter half of each of said trace periods Yto store Yenergy in said wind- Y ing; and

a Wave-shaping circuit comprising a parallel arrangement of a resistor and a capacitor connected across said winding to effect a substantially parabolic current flow through said Winding with substantially no current flow at the middle of each of said trace periods.

3. In a television color image display system including a multiple beam color image reproducing device and deflection means `for deflecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said beams at all points of said raster comprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth wave;

means including a transistor coupling said source to said winding to impress said sawtooth wave upon said winding only during the latter half of each of said trace periods to store energy in said winding; and

a wave-shaping circuit comprising a series arrangement of a resistor and a diode shunted by a capacitor connected across said Winding to effect a substantially parabolic current flow through said winding with substantially no current flow at the middle of each of said trace periods.

4. In a `television color image display system including -a multiple beam color image reproducing device and deflection means for deflecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination -for converging said beams .at all points of said raster comprising;

a dynamic convergence electromagnet having an energizing winding;

a source of a sawtooth wave;

means including a transistor coupling said source to said winding to impress said sawtooth wave upon said winding only during the latter half of each of said trace periods to store energy in said winding; and

a wave-shaping circuit comprising a series arrangement of a resistor and a diode shunted by a capacitor connected across said Winding to effect a substantially parabolic current flow through said winding with substantially no current flow at the middle of each of said trace periods, said diode being poled for conduction only during the first -half of each of said trace periods so 'as to minimize current flow through said transistor.

5. In a television color image display system including 9 a multiple beam color image reproducing device and deection means for deecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said beams at all points of said raster comprising;

a plurality of respective dynamic convergence electromagnets for said beams, each of said electromagnets having an energizing winding;

a source of a sawtooth wave;

means including a transistor coupling said source to two of said windings effectively in parallel to impress said sawtooth wave upon said two windings only during the latter half of each of said trace periods to store energy in said two windings; and

a wave-shaping circuit connected effectively across said two windings to effect a substantially parabolic current flow -through said two windings with substantially no current flow at the middle of each of said trace periods.

6. In a television color image display system including a multiple beam color image reproducing device and deflection means for deflecting said beams in a seires of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said beams at all points of said raster comprising;

a plurailty of respective dynamic convergence electromagnets for said beams, each of said electromagnets having an energizing winding;

a source of a sawtooth wave;

means including a transistor coupling said source to two of said windings effectively in parallel to impress said sawtooth wave upon said two windings only during the later half of each of said trace periods to store energy in said two windings;

a wave-shaping circuit connected effectively across said two windings to effect a Substantially parabolic curren-t flow through said two windings with substantially no current flow at the middle of each of said trace periods;

means connected to control the amplitude of said sawtooth wave impressed upon said two windings; and

means connected to differentially apportion said sawtooth wave between said two windings.

7. In a television color image display system including a multiple beam color image reproducing device and defiection means for deiiecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said beams at all points of said raster comprising;

a plurailty of respective dynamic convergence electromagnets for said beams, each of said electromagnets having an energizing winding;

a source of a sawtooth wave;

means including a transistor coupling said source to two of said windings effectively in parallel to impress said sawtooth wave upon said two windings only during the latter half of each of said trace periods to storage energy in said two windings;

a wave-shaping circuit connected effectively across said two windings to effect a substantially parabolic current flow through said two windings with substantially no current fiow at the middle of each of said trace periods;

means connected to control the amplitude of said sawtooth wave impressed upon said two windings;

means connected to differentially apportion said sawtooth wave between said two windings;

a source of pulses coupled to said two windings; and

means connected to differentially apportion said pulses between said two windings.

8. In a television color image display system including a three beam color image reproducing device and lif) defiection means for deliecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said three beams at all points of said raster comprising;

three respective dynamic convergence electromagnets for said three beams, each of said electromagnets having lan energizing winding;

a source of a sawtooth wave;

means including a first transistor coupling said source to two of said three windings effectively in parallel to impress -said sawtooth wave upon said two windings only during the latter half of each of said trace periods to store energy in said two windings;

a first wave-shaping circuit lconnected effectively across said two windings to effect a substantially parabolic current flow through said two windings with substantially no current flow at the middle of each of said trace periods;

means including a second transistor coupling said sawtooth wave source to the third one of said three windings to impress said sawtooth wave upon said third winding only during the latter half of each of said trace periods to store energy in said third winding; and

a second wave-shaping circuit yconnected across said third winding to effect a substantially parabolic current flow through said third winding with substantially no current flow at the middle of each of said trace periods.

9. In a television color image display system including la .three beam color image reproducing device Iand deflection means for defiecting said Ibeams in a series of vertically spaced horizontal lines during successive beam trace periods ,to form a raster,

the combination for converging `said Ithree beams at all points of said raster comprising;

three respective dynamic convergence electromagnets for said three beams, each of said electromagnets having Ian energizing winding;

a source of a sawtooth wave;

means including a first transistor coupling said source to two of Said .three windings effectively in parallel to limpress said sawtooth wave upon said Itwo windings only during the latter half of each of said trace periods .to store energy in said two windings;

a first wave-shaping circuit connected effectively across said two windings to effect a substantially parabolic current flow through said two windings with substantially no current flow at the middle of each of said trace periods;

means connected to control the amplitude of said sawtooth wave impressed upon said two windings;

means connected to differentially apportion said sawtooth wave between said two windings;

means including .a second ltransistor coupling said sawtooth wave source to .the .third one of said three windings to impress said sawtooth wave upon said third winding only during the latter half of each of said trace periods to store energy in said third winding;

a second Wave-.shaping circuit connected across said third winding to effect a substantially parabolic curlrenlt flow through said third wind-ing with substan- .tially no current iiow at the middle of each of said trace periods; and

means connected to control the amplitude of said sawtooth wave impressed upon said .third winding.

10. In a television color image display system including a .three beam color image reproducing device `and ideiiection means for delieoting said beams in a series of vertically spaced horizontal llines during successive beam :trace periods to form a raster,

.the combina-tion for converging said three beams at all points of said raster comprising; :three respective dynamic convergence electromagnets l l for said .three beams, each `of said electromagnets |having an energizing winding;

-a source of a sawtooth wave;

means including a first transistor coupling said source to two of said three windings effectively in parallel to impress said sawtooth -wave upon said two windings only during `the latter half lof each of said trace periods to store energy in said two windings;

a first wave-shaping circuit comprising ,a parallel `arrangement of a resistor and a capacitor connected effectively across said two windings to effect a substantially parabolic current flow through said two windings with substantially no current flow .at the middle of each of said trace periods;

means connected to control the amplitude of said sawtooth wave impressed upon said two windings;

means connected to differentially apportion said sawtooth wave between said two wind-ings;

means including a second transistor coupling said sawtooth wave source to the third one of said three windings to impress said sawtooth wave upon said third winding only during the la-tter half of each of said Itrace periods to store energy in said third windma;

a second wave-shaping circuit comprising a parallel .arrangement of a resistor and a capacitor connected across `said third winding to effect a substantially parabolic current flow through said third winding with substantially no current flow at the middle of each of said trace periods; and

means connected to control the amplitude of said sawtooth wave impressed upon said third winding.

11. In a television color image display system including a three beam color image reproducing device and deflection means for deflecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said three beams at all points of said raster comprising;

three respective dynamic convergence electromagnets for said three beams, each of said electromagnets having an energizing winding;

a source of a sawtooth wave;

means including a first transistor coupling said source to two of said three windings effectively in parallel .to impress said sawtooth wave upon said two windings only during the lat-ter half of each of said trace periods to store energy in said two windings;

a first wave-shaping circuit connected effectively across said two windings to effect a substantially parabolic current flow through said two windings with substantially no current flow at the middle of each of said trace periods;

means connected to control Ithe amplitude of said sawtooth wave impressed upon said two wind-ings;

means connected to differentially Iapportion said sawtooth wave between said two windings;

means including a second ,transistor coupling said sawtoo-th Wave source to the third -one of said three windings to impress said `sawtooth wave upon said third winding only during the latter half of each of said trace periods to store energy in said third winding;

la second wave-shaping circuit connected across said third winding to effect a substantially parabolic current flow through said .third winding with substantially no current iiow at the middle of each of said 'trace periods;

at least -one of said first and second wave-shaping circuits comprising ia series yarrangement of a resistor .and a diode shunted by a capacitor; and

means connected to control Ithe amplitude of said sawtooth wave impressed upon said third winding.

l12. In a television color image display system including a three beam color image reproducing device and deflection means for deilecting said beams in a series of vertically spaced horizontal lines during successive beam trace periods to form a raster,

the combination for converging said three beams at yall points of said raster comprising;

three respective dynamic convergence electromagnets for said three beams, each of said electromagnets having an energizing winding;

a source of a sawtooth wave;

means incluuding a first transistor coupling said source to two of said three windings effectiveliy in parallel to impress said saw-tooth wave upon said two windings only during the latter half of each of said trace periods Ito store energy in said two windings;

a first Wave-Shaping circuit comprising a parallel arrangement of a resistor and a capacitor connected effectively across said two windings to effect a substan-tially parabolic current flow through said two windings with substantially no current flow at the middle of each of said trace periods;

means connected to control the amplitude of said sawtooth lwave impressed upon said two windings;

means connected to differentially apportion said sawtooth wave between said two windings;

means including a second transistor coupling said sawtooth wave source to the third one of said three windings to impress said sawtooth wave upon said third winding only during the latte-r half of each of said trace periods to store energy in said third windma;

a second wave-shaping circuit comprising a series arrangement of a resistor and a diode shunted by a capacitor connected across said third winding to effect a substantially parabolic current flow through said third winding with substantially no current ow at the middle `of each of' said trace periods, said diode being poled for conduction only during the first half of each of said periods so as to minimize current ow through said second transistor; and

means connected to control the amplitude of said sawtooth wave impressed upon said third winding.

No references cited.

DAVID G. yREDINBAUGH, Primary Examiner.

T. A. GALLAGHER, Assistant Examiner. 

1. IN A TELEVISION COLOR IMAGE DISPLAY SYSTEM INCLUDING A MULTIPLE BEAM COLOR IMAGE REPRODUCING DEVICE AND DEFLECTION MEANS FOR DEFLECTING SAID BEAMS IN A SERIES OF VERTICALLY SPACED HORIZONTAL LINES DURING SUCCESSIVE BEAM TRACE PERIODS ON FORM A RASTER, THE COMBINATION FOR CONVERGING SAID BEAMS AT ALL POINTS OF SAID RASTER COMPRISING; A DYNAMIC CONVERGENCE ELECTROMAGNET HAVING AN ENERGIZING WINDING; A SOURCE OF A SAWTOOTH WAVE; MEANS INCLUDING A TRANSISTOR COUPLING SAID SOURCE TO SAID WINDING TO IMPRESS SAID SAWTOOTH WAVE UPON SAID WINDING ONLY DURING THE LATTER HALF OF EACH OF SAID TRACE PERIODS TO STORE ENERGY IN SAID WINDING; AND A WAVE-SHAPING CIRCUIT CONNECTED ACROSS SAID WINDING TO EFFECT TO SUBSTANTIALLY PARABOLIC CURRENT FLOW THROUGH SAID WINDING WITH SUBSTANTIALLY NO CURRENT FLOW AT THE MIDDLE OF EACH OF SAID TRACE PERIODS. 